The present invention relates to a magnetic resonance spectroscopic system for measuring information such as the spin density, chemical shift, etc., of certain atomic nuclei present in an object under examination based on magnetic resonance (MR).
Conventional magnetic resonance spectroscopic systems obtain the sectional image of a desired planar slice S in a sample P under examination as shown in FIG. 8 of the accompanying drawings. There has been an increasing demand for extracting an MR signal of only a localized area or volume (such as a cardiac muscle, an arm muscle, a leg muscle, or the like) in the slice S, and obtaining the frequency spectrum of a resonance signal by way of magnetic resonance spectroscopy for medical diagnosis.
There are known two methods, described below, for extracting an MR signal of only such a localized volume.
One method is known as localized nuclear magnetic resonance spectroscopy as disclosed in U.S. Pat. No. 4,480,228. According to this method, as shown in FIG. 9 of the accompanying drawings, a localized uniform field Bo' is produced in a static magnetic field Bo, and magnetic resonance is caused only in that localized uniform field Bo' to detect an MR signal. With this method, however, it is necessary to vary a coil current range in order to change the distribution of the static field. Moreover, the arrangement is complex and the measuring process is tedious and time-consuming since the sample must be varied in position.
The other method is known as a surface coil method. A surface coil is disposed on the surface of a target region of a sample or object to be examined, and a signal as shown in FIG. 10 is obtained from the surface coil. Then, only an intensive MR signal in an area including a central portion D1 of the obtained signal at a depth in the direction D is extracted and used as an MR signal of a localized area or volume. This method is effective in receiving a signal from the surface of the sample and its neighboring area. However, since signals from deeper areas are weak in intensity, no sufficient MR signal can be obtained from such deeper areas.